diff --git a/Cargo.lock b/Cargo.lock
index 3f45501c79..952d4d2bc1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -37,6 +37,17 @@ version = "0.4.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "739f4a8db6605981345c5654f3a85b056ce52f37a39d34da03f25bf2151ea16e"
 
+[[package]]
+name = "ahash"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f200cbb1e856866d9eade941cf3aa0c5d7dd36f74311c4273b494f4ef036957"
+dependencies = [
+ "getrandom 0.2.2",
+ "once_cell",
+ "version_check",
+]
+
 [[package]]
 name = "aho-corasick"
 version = "0.7.15"
@@ -1376,7 +1387,7 @@ checksum = "e8a70f1e87a3840ed6a3e99e02c2b861e4dbdf26f0d07e38f42ea5aff46cfce2"
 dependencies = [
  "bitflags",
  "gpu-descriptor-types",
- "hashbrown",
+ "hashbrown 0.9.1",
  "tracing",
 ]
 
@@ -1401,7 +1412,17 @@ version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
 dependencies = [
- "ahash",
+ "ahash 0.4.7",
+]
+
+[[package]]
+name = "hashbrown"
+version = "0.11.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ab5ef0d4909ef3724cc8cce6ccc8572c5c817592e9285f5464f8e86f8bd3726e"
+dependencies = [
+ "ahash 0.7.2",
+ "bumpalo",
 ]
 
 [[package]]
@@ -1497,7 +1518,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "824845a0bf897a9042383849b02c1bc219c2383772efcd5c6f9766fa4b81aef3"
 dependencies = [
  "autocfg 1.0.1",
- "hashbrown",
+ "hashbrown 0.9.1",
 ]
 
 [[package]]
@@ -2950,6 +2971,7 @@ name = "roc_collections"
 version = "0.1.0"
 dependencies = [
  "bumpalo",
+ "hashbrown 0.11.2",
  "im 14.3.0",
  "im-rc 14.3.0",
  "wyhash",
@@ -3181,6 +3203,7 @@ name = "roc_mono"
 version = "0.1.0"
 dependencies = [
  "bumpalo",
+ "hashbrown 0.11.2",
  "indoc 0.3.6",
  "linked-hash-map",
  "maplit",
diff --git a/compiler/collections/Cargo.toml b/compiler/collections/Cargo.toml
index 04dee2c3b5..060747e78a 100644
--- a/compiler/collections/Cargo.toml
+++ b/compiler/collections/Cargo.toml
@@ -10,3 +10,4 @@ im    = "14" # im and im-rc should always have the same version!
 im-rc = "14" # im and im-rc should always have the same version!
 wyhash = "0.3"
 bumpalo = { version = "3.6.1", features = ["collections"] }
+hashbrown = { version = "0.11.2", features = [ "bumpalo" ] }
diff --git a/compiler/collections/src/all.rs b/compiler/collections/src/all.rs
index 18cd19f554..a50a8febcb 100644
--- a/compiler/collections/src/all.rs
+++ b/compiler/collections/src/all.rs
@@ -28,6 +28,8 @@ pub type SendMap<K, V> = im::hashmap::HashMap<K, V, BuildHasher>;
 
 pub type SendSet<K> = im::hashset::HashSet<K, BuildHasher>;
 
+pub type BumpMap<'a, K, V> = hashbrown::HashMap<K, V, BuildHasher, hashbrown::BumpWrapper<'a>>;
+
 pub fn arena_join<'a, I>(arena: &'a Bump, strings: &mut I, join_str: &str) -> String<'a>
 where
     I: Iterator<Item = &'a str>,
diff --git a/compiler/mono/Cargo.toml b/compiler/mono/Cargo.toml
index 49d240ca8d..2123562c9a 100644
--- a/compiler/mono/Cargo.toml
+++ b/compiler/mono/Cargo.toml
@@ -16,6 +16,7 @@ roc_solve = { path = "../solve" }
 roc_problem = { path = "../problem" }
 ven_pretty = { path = "../../vendor/pretty" }
 bumpalo = { version = "3.6.1", features = ["collections"] }
+hashbrown = { version = "0.11.2", features = [ "bumpalo" ] }
 ven_ena = { path = "../../vendor/ena" }
 linked-hash-map = "0.5.4"
 
diff --git a/compiler/mono/src/ir.rs b/compiler/mono/src/ir.rs
index 1957cfaa2f..00202f42a2 100644
--- a/compiler/mono/src/ir.rs
+++ b/compiler/mono/src/ir.rs
@@ -6,7 +6,7 @@ use crate::layout::{
 };
 use bumpalo::collections::Vec;
 use bumpalo::Bump;
-use roc_collections::all::{default_hasher, MutMap, MutSet};
+use roc_collections::all::{default_hasher, BumpMap, MutMap, MutSet};
 use roc_module::ident::{ForeignSymbol, Lowercase, TagName};
 use roc_module::low_level::LowLevel;
 use roc_module::symbol::{IdentIds, ModuleId, Symbol};
@@ -126,8 +126,8 @@ pub struct Proc<'a> {
 pub enum HostExposedLayouts<'a> {
     NotHostExposed,
     HostExposed {
-        rigids: MutMap<Lowercase, Layout<'a>>,
-        aliases: MutMap<Symbol, Layout<'a>>,
+        rigids: BumpMap<'a, Lowercase, Layout<'a>>,
+        aliases: BumpMap<'a, Symbol, Layout<'a>>,
     },
 }
 
@@ -1833,7 +1833,8 @@ fn specialize_external<'a>(
     let host_exposed_layouts = if host_exposed_variables.is_empty() {
         HostExposedLayouts::NotHostExposed
     } else {
-        let mut aliases = MutMap::default();
+        let mut aliases =
+            hashbrown::HashMap::with_hasher_in(default_hasher(), hashbrown::BumpWrapper(env.arena));
 
         for (symbol, variable) in host_exposed_variables {
             let layout = layout_cache
@@ -1843,7 +1844,10 @@ fn specialize_external<'a>(
         }
 
         HostExposedLayouts::HostExposed {
-            rigids: MutMap::default(),
+            rigids: hashbrown::HashMap::with_hasher_in(
+                default_hasher(),
+                hashbrown::BumpWrapper(env.arena),
+            ),
             aliases,
         }
     };